The present invention relates generally to satellite communication systems and in particular to a new architecture for a Time Division Multiple Access (TDMA) system for carrying circuit data, packet data, and Asynchronous Transfer Mode (ATM) cells in a common framework.
Satellite TDMA systems have greatly evolved over the years. Earlier satellite TDMA systems were primarily designed to carry voice/speech signals. As the size and number of data applications grew, satellite TDMA systems were then used to interconnect corporate Local Area Networks (LANs). Now with the advent of the INTERNET, satellite TDMA systems are being used to interconnect gateways between networks spanning the entire globe. Along with the evolution of satellite systems, the transmission characteristics of terrestrial, wireless, and satellite environments have also changed due to advances in optic fiber, new coding and signal processing techniques, in addition to faster and cheaper hardware. These combined changes have in turn lead to a change in nature of networking protocols. For example, for data communications, protocols have evolved from the X.25, to Frame Relay, to ATM protocols.
As a result of the change in the nature of traffic carried by satellite TDMA systems, the satellite TDMA systems must now be capable of meeting the specific individual requirements of the types of traffic being carried by the satellite systems. This is particularly true with the ATM communication protocol in which different classes of service (e.g., Constant Bit Rate (CBR), Real Time Variable Bit Rate (RTVBR), Non Real Time Variable Bit
Rate (NRT-VBR), Unspecified Bit Rate (JBR), Available Bit Rate (ABR) all require a different quality of service commitment from any network carrying these different types of ATM data. For example, it may be desirable to deliver a voice data packet even if the packet contains a few bit errors because the overall message content is not severely degraded and is still capable of being understood. On the other hand, if there are any errors in the header of a data packet, the data packet cannot be correctly delivered.
Furthermore, data traffic is inherently bursty in nature. In other words, the time between transmissions, the length of a transmission, and the amount of data in the transmission, can vary greatly. As a result, newer communication systems require the capability of providing bandwidth-on-demand. Therefore, TDMA systems should now be more flexible and be able to adapt to the different traffic characteristics of various communication protocols.
Directly contrasting modern communications' need for bandwidth on demand is the fact that satellite systems are bandwidth limited. Due to the bandwidth constraints of satellite communications, it is important to limit the use of coding to only those times when it is needed. For example, additional coding is justified when a communication link experiences fading or when the particular service type requires it. Conventionally, most satellite systems are designed to provide the performance required under worst case conditions. As a result, conventional satellite systems waste bandwidth under normal operating conditions when the additional coding is not required.
There are several TDMA systems currently used in satellite communications systems. The most common system is the INTELSAT TDMA system. In addition, several other systems have based their design on the INTELSAT system. The INTELSAT system was designed primarily to carry voice traffic communications. Some VSAT systems carry Internet data traffic. However, currently there are no systems which can carry ATM, packet data, and voice traffic in an integrated fashion. This in turn results in wasted bandwidth from these systems and inefficient use of satellite resources.